Implement unmapped activity and missing data warning section

Use a SliverToBoxAdapter wrapping an AnimatedSize or custom expansion widget — avoid ExpansionTile if its styling conflicts with design tokens, as it can be difficult to override comprehensively. The liveRegion announcement is tied to the widget appearing in the tree; wrap the section in a Semantics with liveRegion: true and ensure the parent rebuilds on state change (BlocBuilder). For the amber colour, use the design token AppColors.warningAmber (or equivalent) — never hardcode hex values. Remediation hints come from the server DTO (UnmappedTypeWarning.remediationHint); if the hint is empty, show a generic fallback: 'Contact your coordinator to update the activity type mapping.' Keep the warning item layout simple: Column with CrossAxisAlignment.start, no nested BLoC providers.

Widget tests: render with 0 warnings and verify section is absent from widget tree; render with 2 warnings (collapsed default) and verify header text and collapsed state; render with 5 warnings (expanded default) and verify all warning items visible; tap toggle and verify expanded/collapsed state change; verify Semantics liveRegion is true on the section wrapper; verify amber colour contrast with a helper function asserting ratio >= 4.5:1. Accessibility test verifying touch target size of toggle button >= 44 dp using SemanticsController. Animation test: pump and settle after state change and verify final layout matches expected.